Particle-in-cell simulations Of highly collisional plasmas on the GPU in 1 and 2 dimensions

During 20th century few branches of science have proved themselves to be more industrially applicable than Plasma science and processing. Across a vast range of discharge types and regimes, and through industries spanning semiconductor manufacture, surface sterilisation, food packaging and medicinal treatment, industry continues to find new usefulness in this physical phenomenon well into 21st century. To better cater to this diverse motley of industries there is a need for more detailed and accurate understanding of plasma chemistry and kinetics, which drive the plasma processes central to manufacturing. Extensive efforts have been made to characterise plasma discharges numerically and mathematically leading to the development a number of different approaches. In our work we concentrate on the Particle-In-Cell (PIC) - Monte Carlo Collision (MCC) approach to plasma modelling. This method has for a long time been considered computationally prohibitive by its long run times and high computational resource expense. However, with modern advances in computing, particularly in the form of relatively cheap accelerator devices such as GPUs and co-processors, we have developed a massively parallel simulation in 1 and 2 dimensions to take advantage of this large increase in computing power. Furthermore, we have implemented some changes to the traditional PIC-MCC implementation to provide a more generalised simulation, with greater scalability and smooth transition between low and high (atmospheric) pressure discharge regimes. We also present some preliminary physical and computational benchmarks for our PIC-MCC implementation providing a strong case for validation of our results

Examination of Magnetic Plasma Expulsion

Magnetic plasma expulsion uses a magnetic field distortion to redirect incident charged particles around a certain area for the purposes of shielding. Computational studies are carried out and for certain values of magnetic field, magnetic plasma expulsion is found to effectively shield a sizable area. There are however many plasma behaviors and interactions that must be considered. Applications to a new cryogenic antimatter trap design are discussed

Numerical Studies of Self-modulation Instability in the Beam-Driven Plasma Wakefield Experiments

Department of PhysicsThe plasma wakefield accelerator is one of promising and advanced particle accelerator models. It can make particle accelerator more compact and cheaper. A beam bunch propagating through plasma excites the plasma wakefield at some conditions. The optimum wake is obtained for k_p*??_z = sqrt(2) and k_p*??_r ??? 1. Where k_p is plasma wave number and ??_z (or ??_r) is RMS beam length (or RMS beam radius). But we are interested in using CERN???s long and high-energy proton beams. The CERN???s proton beams are much longer (~12 cm) than the optimum driving beam length (in order of plasma wavelength ??_p). Here we focus on the instability which occurs based on the interaction between beam and plasma electrons. By this instability, the long driving beam is modulated along the propagation direction, so it makes the beam satisfy the optimum size for excitation of plasma waves. What we should know is that the plasma oscillation which is initially and axi-symmetrically excited by beam head will seed self-modulation of driving beam. Therefore, we first study fundamental theories of excitation of plasma waves by the charged particle beam. It???s about the response of plasma electrons to driving beam. The driving beam doesn???t interact with and only affects plasma. Here excited plasma wakefields should be considered. As the next step, the dynamics of plasma wakefield accelerator is introduced. Evolution of beam envelope in time could result in beam centroid offset or radius pinching. Where the two phenomena, centroid offset and radius pinching of the beam in plasma are called ???Self-modulation instability??? and ???Hose instability???. Those two instabilities compete each other. As the last step, the parameters of Injector Test Facility (ITF) at Pohang Accelerator Laboratory (PAL) is used to demonstrate the self-modulation instability.ope

Plasma propulsion simulation using particles

This perspective paper deals with an overview of particle-in-cell / Monte Carlo collision models applied to different plasma-propulsion configurations and scenarios, from electrostatic (E x B and pulsed arc) devices to electromagnetic (RF inductive, helicon, electron cyclotron resonance) thrusters, with an emphasis on plasma plumes and their interaction with the satellite. The most important elements related to the modeling of plasma-wall interaction are also presented. Finally, the paper reports new progress in the particle-in-cell computational methodology, in particular regarding accelerating computational techniques for multi-dimensional simulations and plasma chemistry Monte Carlo modules for molecular and alternative propellan

A generalised formulation of G-continuous Bezier elements applied to non-linear MHD simulations

The international tokamak ITER is progressing towards assembly completion and first-plasma operation, which will be a physics and engineering challenge for the fusion community. In the preparation for ITER experimental scenarios, non-linear MHD simulations are playing an essential role to actively understand and predict the behaviour and stability of tokamak plasmas in future fusion power plant. The development of MHD codes like JOREK is a key aspect of this research effort, and provides invaluable insight into the plasma stability and the control of global and localised plasma events, like Edge-Localised-Mode and disruptions. In this paper, we present an operational implementation of a new, generalised formulation of Bezier finite-elements applied to the JOREK code, a significant advancement from the previously G1-continuous bi-cubic Bezier elements. This new mathematical method enables any polynomial order of Bezier elements, with a guarantee of G-continuity at the level of (n−1)/2, for any odd n, where n is the order of the Bezier polynomials. The generalised method is defined, and a rigorous mathematical proof is provided for the G-continuity requirement. Key details on the code implementation are mentioned, together with a suite of tests to demonstrate the mathematical reliability of the finite-element method, as well as the practical usability for typical non-linear tokamak MHD simulations. A demonstration for a state-of-the-art simulation of an Edge-Localised-Mode instability in the future ITER tokamak, with realistic grid geometry, finalises the study.</p

Three-Dimensional Radiative Transfer on a Massively Parallel Computer.

We perform three-dimensional radiative transfer calculations on the MasPar MP-1, which contains 8192 processors and is a single instruction multiple data (SIMD) machine, an example of the new generation of massively parallel computers. To make radiative transfer calculations efficient, we must re-consider the numerical methods and methods of storage of data that have been used with serial machines. We developed a numerical code which efficiently calculates images and spectra of astrophysical systems as seen from different viewing directions and at different wavelengths. We use this code to examine a number of different astrophysical systems. First we image the HI distribution of model galaxies. Then we investigate the galaxy NGC 5055, which displays a radial asymmetry in its optical appearance. This can be explained by the presence of dust in the outer HI disk far beyond the optical disk. As the formation of dust is connected to the presence of stars, the existence of dust in outer regions of this galaxy could have consequences for star formation at a time when this galaxy was just forming. Next we use the code for polarized radiative transfer. We first discuss the numerical computation of the required cyclotron opacities and use them to calculate spectra of AM Her systems, binaries containing accreting magnetic white dwarfs. Then we obtain spectra of an extended polar cap. Previous calculations did not consider the three-dimensional extension of the shock. We find that this results in a significant underestimate of the radiation emitted in the shock. Next we calculate the spectrum of the intermediate polar RE 0751+14. For this system we obtain a magnetic field of $\sim$10 MG, which has consequences for the evolution of intermediate polars. Finally we perform 3D radiative transfer in NLTE in the two-level atom approximation. To solve the transfer equation in this case, we adapt the short characteristic method and examine different acceleration methods to obtain the source function. These include the ALI method with local and non-local operators, the Ng and the orthomin methods and multi-grid methods. We apply these numerical methods to two problems with and without periodic boundary conditions

Electron transport modeling in gas and liquid media for application in plasma medicine

Emerging plasma technologies, such as plasma medicine, rely on the transport of plasma species across gas-liquid interfaces to achieve their function. Recent studies have identified that, while poorly understood at present, electron transport through the interface is an important driver of plasma chemistry in plasma medicine. In order to understand this fundamental transport, so to facilitate understanding and future optimisation of plasma technologies, a modeling framework for electron transport simulations across gas-liquid interfaces has been developed. This modeling framework has been been applied to noble liquids, such as argon and xenon, and the first steps have been made towards application to a biomolecule system involving tetrahydrofuran. This research has extended previous approaches to electron fluid modeling in the gas phase to propose a fluid model for electron transport in gas and liquid media based on four moments of the Boltzmann kinetic equation. The model was benchmarked against kinetic solutions of electron transport to validate the applicability of the model to describe non-local electron transport phenomena in both gas and liquids, given that appropriate and accurate input data is available. To assess the impact of employing steady-state collision and closure input data in electron fluid models, non-equilibrium velocity distribution functions, computed via multi-term solution of the Boltzmann equation for benchmark calculations, were studied. The dependence of the proposed model's input transport data on the background medium density was examined in this research. By examining how electron momentum and energy transfer occurs due to collisions in gas and liquid extremes, an approximation method was proposed to generate input transport data at intermediate densities for which data is required, but not available, for modeling interfacial transport. The proposed approximation was benchmarked against analytic simple liquids and experimental data measured in cryogenic argon and xenon to verify the applicability of the proposed approach. Simulations of electron transport between gas and liquid argon, and vice versa, was performed by applying both the proposed fluid model and input data approximation method. Comparisons of the abilities of modeling methods to resolve realistic non-local transport were studied, and the stark differences between using electron-liquid transport data compared to simply scaling up electron-gas transport data were discussed. Application of this modeling framework to dual-phase simple liquid particle detector apparatus was demonstrated. Finally, application of the developed modeling framework was made to electron transport in tetrahydrofuran. To do so, a complete gas phase electron scattering cross section set was assembled and analysed using available experimental and theoretical data. Modifications of gas phase scattering to a simulated liquid phase were made using available experimental data. Comparison of streamer formation and propagation in both gaseous and simulated liquid tetrahydrofuran was studied to demonstrate applicability of the framework developed in this research to electron transport in biologically relevant soft-condensed matter

Generation, transport and focusing of high-brightness heavy ion beams

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (p. 195-201).The Neutralized Transport Experiment (NTX) has been built at the Heavy Ion Fusion Virtual National Laboratory. NTX is the first successful integrated beam system experiment that explores various physical phenomena, and determines the final spot size of a high intensity ion beam on a scaled version of a Heavy Ion Fusion driver. The final spot size is determined by the conditions of the beam produced in the injector, the beam dynamics in the focusing lattice, and the plasma neutralization dynamics in the final transport. A high brightness ion source using an aperturing technique delivers 25 mA of single charged potassium ion beam at 300 keV and a normalized edge emittance of 0.05 r-mm-mr. The ion beam is injected into a large bore magnetic quadrupole lattice, which produces a 20 mm radius beam converging at 20 mr. The converging ion beam is further injected into a plasma neutralization drift section where it is compressed ballistically down to a 1 mm spot size.(cont.) NTX provides the first experimental proof of plasma neutralized ballistic transport of a space-charge dominated ion beam, the information about higher order aberration effects on the spot size, the validation of numerical tools based on excellent agreement between measurements and numerical simulations over a broad parameter regime, and the development of new diagnostics to study the ion beam dynamics. The theoretical and experimental results are presented on the beam dynamics in the ion diode, downstream quadrupole lattice, and final neutralized transport.by Enrique Henestroza.Ph.D